System for providing a continuous motion sequential lateral solidification

ABSTRACT

A method and system for processing an amorphous silicon thin film sample to produce a large grained, grain boundary-controlled silicon thin film. The film sample includes a first edge and a second edge. In particular, using this method and system, an excimer laser is used to provide a pulsed laser beam, and the pulse laser beam is masked to generate patterned beamlets, each of the patterned beamlets having an intensity which is sufficient to melt the film sample. The film sample is continuously scanned at a first constant predetermined speed along a first path between the first edge and the second edge with the patterned beamlets. In addition, the film sample is continuously scanned at a second constant predetermined speed along a second path between the first edge and the second edge with the patterned beamlets.

NOTICE OF GOVERNMENT RIGHTS

[0001] The U.S. Government has certain rights in this invention pursuantto the terms of the Defense Advanced Research Project Agency awardnumber N66001-98-1-8913.

FIELD OF THE INVENTION

[0002] The present invention relates to a method and system forprocessing a thin-film semiconductor material, and more particularly toforming large-grained grain boundary-location controlled semiconductorthin films from amorphous or polycrystalline thin films on a substrateusing laser irradiation and a continuous motion of the substrate havingthe semiconductor film being irradiated.

BACKGROUND INFORMATION

[0003] In the field of semiconductor processing, there have been severalattempts to use lasers to convert thin amorphous silicon films intopolycrystalline films. For example, in James Im et al., “Crystalline SiFilms for Integrated Active-Matrix Liquid-Crystal Displays,” 11 MRSBulletin 39 (1996), an overview of conventional excimer laser annealingtechnology is described. In such conventional system, an excimer laserbeam is shaped into a long beam which is typically up to 30 cm long and500 micrometers or greater in width. The shaped beam is stepped over asample of amorphous silicon to facilitate melting thereof and theformation of grain boundary-controlled polycrystalline silicon upon theresolidification of the sample.

[0004] The use of conventional excimer laser annealing technology togenerate polycrystalline silicon is problematic for several reasons.First, the polycrystalline silicon generated in the process is typicallysmall grained, of a random micro structure (i.e., poor control of grainboundaries), and having a nonuniform grain sizes, therefore resulting inpoor and nonuniform devices and accordingly, low manufacturing yield.Second, in order to obtain acceptable quality grain boundary-controlledpolycrystalline thin films, the manufacturing throughput for producingsuch thin films must be kept low. Also, the process generally requires acontrolled atmosphere and preheating of the amorphous silicon sample,which leads to a reduction in throughput rates. Accordingly, thereexists a need in the field to generate higher quality thinpolycrystalline silicon films at greater throughput rates. Therelikewise exists a need for manufacturing techniques which generatelarger and more uniformly microstructured polycrystalline silicon thinfilms to be used in the fabrication of higher quality devices, such asthin film transistor arrays for liquid crystal panel displays.

SUMMARY OF THE INVENTION

[0005] An object of the present invention is to provide techniques forproducing large-grained and grain boundary location controlledpolycrystalline thin film semiconductors using a sequential lateralsolidification process and to generate such silicon thin films in anaccelerated manner.

[0006] At least some of these objects are accomplished with a method andsystem for processing an amorphous or polycrystalline silicon thin filmsample into a grain boundary-controlled polycrystalline thin film or asingle crystal thin film. The film sample includes a first edge and asecond edge. In particular, using this method and system, a laser beamgenerator is controlled to emit a laser beam, and portions of this laserbeam are masked to generate patterned beamlets, each of the beamletshaving an intensity which is sufficient to melt the film sample. Thefilm sample is continuously scanned at a first constant predeterminedspeed along a first path between the first edge and the second edge bythe patterned beamlets. In addition, the film sample is continuouslyscanned at a second constant predetermined speed along a second pathbetween the first edge and the second edge by the patterned beamlets.

[0007] In another embodiment of the present invention, the film sampleis continuously translated in a first direction so that the fixedpatterned beamlets continuously irradiate successive first portions ofthe film sample along the first path. The first portions are meltedwhile being irradiated. In addition, the film sample is continuouslytranslated in a second direction so that the fixed patterned beamletsirradiate successive second portions of the film sample along the secondpath. The second portions are melted while being irradiated.Furthermore, after the film sample is translated in the first directionto irradiate a next successive portion of the first path of the filmsample, the first portions are cooled and resolidified, and after thefilm sample is translated in the second direction to irradiate a nextsuccessive portion of the second path of the film sample, the secondportions are cooled and resolidified.

[0008] In yet another embodiment of the present invention, the filmsample is positioned so that the patterned beamlets impinge at a firstlocation outside of boundaries of the film sample with respect to thefilm sample. Also, the film sample can be microtranslated from the firstlocation to a second location before the film sample is scanned alongthe second path, starting from the second location.

[0009] In a further embodiment of the present invention, after the filmsample is scanned along the second path, the film sample is translatedso that the beamlets impinge a third location which is outside theboundaries of the film sample microtranslated. Thereafter, the filmsample can be stepped so that the impingement of the beamlets moves fromthe third location to a fourth location, the fourth location beingoutside of the boundaries of the film sample. Then, the film sample ismaintained with the patterned beamlets impinging on the fourth locationuntil the film sample stops vibrating and after the movement of the filmsample ceases.

[0010] In another embodiment of the present invention, the film sampleis continuously scanned in a first direction so that the fixed positionbeamlets scan the first path, and then in a second direction so that thefixed position beamlets scan the second path. After the film sample istranslated in the first direction, it is continuously translated at thefirst constant predetermined speed in a second direction so that thepatterned beamlets irradiate the first successive portions of the filmsample along the second path, the second direction being opposite to thefirst direction. Then, the film sample is microtranslated so that theimpingement of the beamlets moves from the first location to a secondlocation, the second location being outside of boundaries of the filmsample. Thereafter, the film sample is continuously translated at thesecond constant predetermined speed in a first direction so that thepatterned beamlets irradiate second successive portions of the filmsample along the second path until the beamlets impinge on the secondlocation, the first direction being opposite to the second direction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1a shows a diagram of an exemplary embodiment of a system forperforming a continuous motion solidification lateral solidification(“SLS”) according to the present invention.

[0012]FIG. 1b shows an embodiment of a method according of the presentinvention for providing the continuous motion SLS which may be utilizedby the system of FIG. 1a.

[0013]FIG. 2a shows a diagram of a mask having a dashed pattern.

[0014]FIG. 2b shows a diagram of a portion of a crystallized siliconfilm resulting from the use of the mask shown in FIG. 2a in the systemof FIG. 1a.

[0015]FIG. 3a shows a diagram of a mask having a chevron pattern.

[0016]FIG. 3b shows a diagram of a portion of a crystallized siliconfilm resulting from the use of the mask shown in FIG. 3a in the systemof FIG. 1a.

[0017]FIG. 4a shows a diagram of a mask having a line pattern.

[0018]FIG. 4b shows a diagram of a portion of a crystallized siliconfilm resulting from the use of the mask shown in FIG. 4a in the systemof FIG. 1a.

[0019]FIG. 5a shows an illustrative diagram showing portions ofirradiated areas of a silicon sample using a mask having the linepattern.

[0020]FIG. 5b shows an illustrative diagram of the portions of theirradiated areas of a silicon sample using a mask having a line patternafter initial irradiation and sample translation has occurred, and aftera single laser pulse during the method illustrated in FIG. 1b.

[0021]FIG. 5c shows an illustrative diagram of the portions of thecrystallized silicon film after a second irradiation has occurred whichwas generated using the method illustrated in FIG. 1b.

[0022]FIG. 6a shows a mask having a diagonal line pattern.

[0023]FIG. 6b a diagram of a portion of a crystallized silicon filmresulting from the use of the mask shown in FIG. 6a in the system ofFIG. 1a;

[0024]FIG. 7 shows another embodiment of a method according of thepresent invention for providing the continuous motion SLS which may beutilized by the system of FIG. 1a.

[0025]FIG. 8 shows a flow diagram illustrating the steps implemented bythe method illustrated in FIG. 1b.

DETAILED DESCRIPTION

[0026] The present invention provides techniques for producing uniformlarge-grained and grain boundary location controlled crystalline thinfilm semiconductors using the sequential lateral solidification process.In order to fully understand those techniques, the sequential lateralsolidification process must first be appreciated.

[0027] The sequential lateral solidification process is a technique forproducing large grained silicon structures through small-scaleunidirectional translation of a sample in having a silicon film betweensequential pulses emitted by an excimer laser. As each pulse is absorbedby the silicon film, a small area of the film is caused to meltcompletely and resolidify laterally into a crystal region produced bythe preceding pulses of a pulse set.

[0028] An advantageous sequential lateral solidification process and anapparatus to carry out that process are disclosed in co-pending patentapplication Ser. No.09/390,537 (the “'537 application”) filed on Sep.3,1999, and assigned to the common assignee, the entire disclosure ofwhich is incorporated herein by reference. While the foregoingdisclosure is made with reference to the particular techniques describedin the '537 application, it should be understood that other sequentiallateral solidification techniques could easily be adapted for the use inthe present invention.

[0029]FIG. 1a shows a system according to the present invention which iscapable of implementing the continuous motion SLS process. As alsodescribed in the '537 application, the system includes an excimer laser110, an energy density modulator 120 to rapidly change the energydensity of a laser beam 111, a beam attenuator and shutter 130 (which isoptional in this system), optics 140, 141, 142 and 143, a beamhomogenizer 144, a lens and beam steering system 145, 148, a maskingsystem 150, another lens and beam steering system 161, 162, 163, anincident laser pulse 164, a thin silicon film sample on a substrate 170,a sample translation stage 180, a granite block 190, a support system191, 192, 193, 194, 195, 196, and a computer 100 which manages X and Ydirection translations and microtranslations of the silicon film sampleand substrate 170. The computer 100 directs such translations and/ormicrotranslations by either a movement of a mask within masking system150 or by a movement of the sample translation stage 180.

[0030] As described in further detail in the '537 application, anamorphous silicon thin film sample is processed into a single orpolycrystalline silicon thin film by generating a plurality of excimerlaser pulses of a predetermined fluence, controllably modulating thefluence of the excimer laser pulses, homogenizing the modulated laserpulses in a predetermined plane, masking portions of the homogenizedmodulated laser pulses into patterned beamlets, irradiating an amorphoussilicon thin film sample with the patterned beamlets to effect meltingof portions thereof irradiated by the beamlets, and controllablytranslating the sample with respect to the patterned beamlets and withrespect to the controlled modulation to thereby process the amorphoussilicon thin film sample into a single or grain boundary-controlledpolycrystalline silicon thin film by the sequential translation of thesample relative to the patterned beamlets and irradiation of the sampleby patterned beamlets of varying fluence at corresponding sequentiallocations thereon. The following embodiments of the present inventionwill now be described with reference to the foregoing processingtechnique.

[0031]FIG. 1b shows an embodiment of a process according of the presentinvention for providing the continuous motion SLS which may utilize thesystem described above. In particular, the computer 100 controls themotion (in the planar X-Y direction) of the sample translation stage 180and/or the movement of the masking system 150. In this manner, thecomputer 100 controls the relative position of the sample 170 withrespect to the pulsed laser beam 149 and the final pulsed laser beam164. The frequency and the energy density of the final pulsed laser beam164 are also controlled by the computer 100.

[0032] As described in co-pending patent application Ser. No. 09/390,535(the “'535 application”) filed on Sep. 3, 1999, and also assigned to thecommon assignee, the entire disclosure of which is incorporated hereinby reference, the sample 170 may be translated with respect to the laserbeam 149, either by moving the masking system 150 or the sampletranslation stage 180, in order to grow crystal regions in the sample170. For example, for the purposes of the foregoing, the length andwidth of the laser beam 149 may be 2 cm in the X-direction by ½ cm inthe Y-direction (e.g., a rectangular shape), but the pulsed laser beam149 is not limited to such shape and size. Indeed, other shapes and/orsizes of the laser beam 149 are, of course, achievable as is known tothose having ordinary skill in the art (e.g., square, triangle, etc.).

[0033] Various masks may also be utilized to create the final pulsedlaser beam and beamlets 164 from the transmitted pulsed laser beam 149.Some examples of the masks are shown in FIGS. 2a, 3 a, 4 a and 6 a, adetailed description of which has already been provided in the '535application. For example, FIG. 2a shows a mask 210 incorporating aregular pattern of slits 220, FIG. 3a shows a mask 310 incorporating apattern of chevrons 320, and FIG. 6a shows a mask 610 incorporating apattern of diagonal lines 620. For the sake of simplicity, providedbelow is a description of the process accordingly to the presentinvention which utilizes a mask 410 (shown in FIG. 4a) incorporating apattern of slits 410, each of which may extend as far across on the mask410 as the homogenized laser beam 149 incident on the mask 410 permits,and should have a width 440 that is sufficiently narrow to prevent anynucleation from taking place in the irradiated region of the sample 170.As discussed in the '535 application, the width 440 may depend on anumber of factors, e.g., the energy density of the incident laser pulse,the duration of the incident laser pulse, the thickness of the siliconthin film sample, the temperature and thermal conductivity of thesilicon substrate, etc.

[0034] In the exemplary embodiment shown in FIB. 1 b, the sample 170 hasthe size of 40 cm in the Y-direction by 30 cm in the X-direction. Thesample 170 is conceptually subdivided into a number of columns (e.g., afirst column 5, a second column 6, etc.), and the location/dimension ofeach column is stored in a storage device of the computer 100, andutilized by the computer 100. Each of the columns is dimensioned, e.g.,2 cm in the X-direction by 40 cm in the Y-direction. Thus, the sample170 may be conceptually subdivided into, e.g., fifteen columns. It isalso conceivable to conceptually subdivide the sample 170 into columnshaving different dimensions (e.g., 3 cm by 40 cm columns, etc.). Whenthe sample 170 is conceptually subdivided into columns, at least a smallportion of one column extending for the entire length of such columnshould be overlapped by a portion of the neighboring column to avoid apossibility of having any unirradiated areas. For example, theoverlapped area may have a width of, e.g.,1 μm.

[0035] After the sample 170 is conceptually subdivided, a pulsed laserbeam 111 is activated (by actuating the excimer laser using the computer100 or by opening the shutter 130) and produces the pulsed laserbeamlets 164 impinging on a first location 20 (from the pulsed laserbeam 149). Then, the sample 170 is translated and accelerated in theforward Y-direction under the control of the computer 100 to reach apredetermined velocity with respect to the fixed position beamlets in afirst beam path 25. Using the equation:

Vmax =Bw•f,

[0036] where Vmax is a maximum possible velocity that the sample 170 canbe moved with respect to the pulsed beamlets 164, Bw is the width of thepattern of the pulsed laser beamlets 164 (or the width of the envelopeof the pulsed beamlets 164), and f is the frequency of the pulsedbeamlets 164, the predetermined velocity Vpred can be determined usingthe following:

Vpred=Vmax—K,

[0037] where K is a constant, and is utilized to avoid a possibility ofhaving any unirradiated areas between adjacent irradiated areas. It isalso possible to use the system according to the present inventionillustrated in FIG. 1a without utilizing the beam attentuator andshutter 130, since (as described below) due to the continuoustranslation of the sample 170, the pulsed beamlets 164 does not have tobe blocked or turned off.

[0038] The pulsed beamlets 164 reach an upper edge 10′ of the sample 170when the velocity of the movement of the sample 170 with respect to thepulsed laser beam 149 reaches the predetermined velocity Vpred. Then,the sample 170 is continuously (i.e., without stopping) translated inthe forward Y-direction at the predetermined velocity Vpred so that thepulsed beamlets 164 continue irradiating successive portions of thesample 170 for an entire length of a second beam path 30. When thepulsed beamlets 164 reach a lower edge 10″ of the sample 170, thetranslation of the sample 170 is slowed with respect to the pulsedbeamlets 164 (in a third beam path 35) to reach a second location 40.After the pulsed beamlets 164 continuously and sequentially irradiatedthe successive portions of the sample 170 along the second beam path 30,these successive portions of the sample 170 are fully melted. It shouldbe noted that after the pulsed beamlets 164 pass the lower edge 10″ ofthe sample 170, a crystalized silicon thin film area 540 (e.g., grainboundary-controlled polycrystalline silicon thin film) forms in theirradiated second beam path 30 area of the sample 170, a portion ofwhich is shown in FIG. 5b. This grain boundary-controlledpolycrystalline silicon thin film area 540 extends for the entire lengthof the second irradiated beam path 30. It should be noted that it is notnecessary to shut down the pulsed laser beam 149 after the pulsedbeamlets 164 have crossed the lower edge 10″ of the sample 170 becauseit is no longer irradiating the sample 170.

[0039] Thereafter, to eliminate the numerous small initial crystals 541that form at melt boundaries 530 and while the location along theY-direction of the pulsed beamlets 164 is fixed, the sample 170 ismicrotranslated for a predetermined distance (e.g., 3 micrometers) inthe X-direction along a fourth beam path 45 to reach a third location47, and is then accelerated in the reverse Y-direction (toward the topedge 10′ of the sample 170) under the control of the computer 100 toreach the predetermined velocity of translation with respect to thepulsed beamlets 164 along a fourth beam path 50. The pulsed beamlets 164reach the lower edge 10″ of the sample 170 when the velocity of thesample 170 with respect to the pulsed beamlets 164 reaches thepredetermined velocity Vpred. The sample 170 is continuously translated(i.e., without stopping) in the reverse Y-direction at the predeterminedvelocity Vpred so that the pulsed beamlets 164 irradiate the sample 170for the entire length of a fifth beam path 55. When the sample 170 istranslated under the control of the computer 100 so that the pulsedbeamlets 164 reach the upper edge 10′ of the sample 170, the continuoustranslation of the sample 170 is again slowed with respect to the pulsedbeamlets 164 (in a sixth beam path 60) to reach a fourth location 65.The result of such irradiation of the fifth beam path 55 is that regions551, 552, 553 of the sample 170 (shown in FIG. 5b) cause the remainingamorphous silicon thin film 542 and the initial crystallized regions 543of the polycrystalline silicon thin film area 540 to melt, while leavingthe central section 545 of the polycrystalline silicon thin film toremain solidified. After the pulsed beamlets 164 continuously andsequentially irradiated the successive portions of the sample 170 alongthe fifth beam path 55, these successive portions of the sample 170 arefully melted. Thus, as a result of the laser beam 149's continuous(i.e., without a stoppage) irradiation of the first column 5 for itsentire length in the fifth beam path 55, the crystal structure whichforms the central section 545 outwardly grows upon solidification ofmelted regions 542, 542 of the thin film which were formed as a resultof the continuous irradiation along the second beam path 30. Thus, adirectionally controlled long grained polycrystalline silicon thin filmis formed on the sample 170 along the entire length of the fifth beampath 55. A portion of such crystallized structure is illustrated in FIG.5c. Therefore, using the continuous motion SLS procedure describedabove, it is possible to continuously form the illustrated crystallizedstructure along the entire length of the column of the sample 170.

[0040] Then, the sample 170 is stepped to the next column 6 to reach afifth location 72 via a seventh beam path 70, and the sample is allowedto settle at that location to allow any vibrations of the sample 170that may have occurred when the sample 170 was stepped to the fifthlocation 72 to cease. Indeed, for the sample 170 to reach the secondcolumn 6, it is stepped approximately 2 cm for the columns having awidth (in the X-direction) of 2 cm. The procedure described above withrespect to the irradiation of the first column 5 may then be repeatedfor the second column 6. In this manner, all columns of the sample 170can be properly irradiated with only a minimal settling time which maybe required for the sample 170 to settle (and thus wait for thevibrations of the sample 170 to stop). Indeed, the only time that may berequired for settling the sample 170 is when the laser has completed theirradiation of an entire column (e.g., the first column 5) of the sample170, and the sample 170 is stepped to the next column (e.g., the secondcolumn 6) of the sample 170. Using the exemplary dimensions of thesample 170 described above (30 cm by 40 cm), since each column isdimensioned 2 cm by 40 cm, there are only 15 columns that must beirradiated for this exemplary sample 170. Accordingly, the number of“step and settle” delays that may occur for the exemplary sample 170 iseither 14 or 15.

[0041] To illustrate the time savings in using the continuous motion SLSprocedure according to the present invention for producing thecrystallized silicon thin film, it is possible that the time it takes totranslate the sample 170 (which has the sample, column and laser beamdimensions discussed above) for the entire lengths in the various travelpaths of the sample 170 is estimated below: the first beam path 25 0.1seconds, the second beam path 30 0.5 seconds (since the sample 170 doesnot have to stop and settle for the entire length of a column, andtranslates continuously), the third beam path 35 0.1 seconds, the fourthbeam path 45 0.1 seconds, the fifth beam path 50 0.1 seconds, the sixthbeam path 55 0.5 seconds (again because the sample 170 does not have tostop and settle for the entire length of a column, and translatescontinu- ously), the seventh beam path 60 0.1 seconds, and the eightbeam path 70 0.1 seconds.

[0042] Thus, the total time that it takes to completely irradiate eachcolumn 5, 6 of the sample is 1.6 seconds (or at most, e.g., 2 seconds).Thus, for 15 columns of the sample 170, the total time that it takes toform the grain boundary-controlled polycrystalline structure thin film(for the entire sample 170) is approximately 30 seconds.

[0043] As indicated above, it is also possible to use differentdimensions and/or shapes for cross-sectional area of the laser beam 149.For example, it is possible to use the pulsed laser beam 149 which hasthe cross-sectional area dimensioned 1 cm by 1 cm (i.e., a squareshape). It should be appreciated that it is advantageous to use thediameter of the pulsed beamlets 164 as one of the dimension parametersof the columns. In this instance, the 30 cm by 40 cm sample 170 may beconceptually subdivided into 30 columns, each column being dimensioned 1cm in the X-direction by 40 cm in the Y-direction (assuming across-section of a diameter of the pattern of the pulsed beamlets 164 of1 cm). Using such a pattern of the pulsed beamlets 164, it may bepossible to increase the predetermined velocity Vpred for translatingthe sample 170, and possibly decrease the total energy of the pulsedlaser beam 149. In this manner, instead of irradiating the sample via 15columns, the system and method according to the present invention wouldirradiate the sample via 30 columns. Even though it may take longer tostep and settle from column to column for 30 columns (as opposed to 15columns described above), the speed of the sample translation may beincreased because, due to the column's smaller width, the intensity ofthe pulsed laser beam 149 can be greater, as a result of concentratingthe laser pulse energy into a smaller beamlet pattern, to provideeffective crystallization of the sample 170, and the total time tocomplete the irradiation of the sample 170 may not be significantlyhigher than that for the sample which has 15 columns.

[0044] According to the present invention, any mask described and shownin the '535 application may be used for the continuous motion SLSprocedure illustrated in FIG. 1b. For example, when the mask 310 is usedin masking system 150, a processed sample (i.e., a portion 350 shown inFIG. 3b having crystallized regions 360) is produced. Each crystalregion 360 will consist of a diamond shaped single crystal region 370and two long grained, directionally controlled grain boundarypolycrystalline silicon regions 380 in the tails of each chevron. Onemay also use a mask 610 (shown in FIG. 6a) incorporating a pattern ofdiagonal slits 620. For this mask 610, when the sample 170 iscontinuously translated in the Y-direction, and the mask 610 is used inthe masking system 150 of FIG. 1 a, a processed sample (a portion 650shown in FIG. 6b having crystallized regions 660) is produced. Eachcrystallized region 660 will consist of long grained, crystallineregions with directionally-controlled grain boundaries 670.

[0045] It is also possible to irradiate the sample 170 along the columnswhich are not parallel to the edges of the square sample 170. Forexample, the columns may extend at approximately 45 degree angle withrespect to the edges of the sample 170. The computer 100 stores startand end points of each column and is capable of performing the procedureshown in FIG. 1b along parallel columns which are slanted at, e.g., 45degrees with respect to the edges of the sample 170. The sample 170 canalso be irradiated along parallel columns which are slanted at otherangles with respect to the edges of the sample 170 (e.g., 60 degrees, 30degrees, etc.).

[0046] In another exemplary embodiment of the method according to thepresent invention which is shown in FIG. 7, the sample 170 isconceptually subdivided into a number of columns. After the sample 170is subdivided, the pulsed laser beam 149 can be turned on (by actuatingthe excimer laser using the computer 100 or by opening the shutter 130)so that it produces the pulsed beamlets 164 which initially impinge onthe first location 20 (similarly to the embodiment illustrated in FIG.1b). Then, the sample 170 is translated and accelerated in theY-direction under the control of the computer 100 to reach thepredetermined sample translation velocity Vpred with respect to thepulsed beamlets 164 in a first beam path 700. The pulsed beamlets 164(and the beamlets) reach an upper edge 10′ of the sample 170 when thevelocity of the translation of the sample 170 with respect to the pulsedlaser beam 149 reaches the predetermined velocity Vpred. Then, thesample 170 is continuously (i.e., without stopping) translated in theY-direction at the predetermined velocity Vpred continuously andsequentially so that the pulsed beamlets 164 irradiate the sample 170for an entire length of a second beam path 705. When the pulsed beamlets164 reach the lower edge 10″ of the sample 170, the translation of thesample 170 is slowed with respect to the pulsed beamlets 164 (in a thirdbeam path 710) to reach a second location 715. It should be noted thatafter the pulsed beamlets 164 pass the lower edge 10″ of the sample 170,the entire portion of the sample 170 along the second beam path 705 hasundergone sequential full melting and solidification.

[0047] The sample 170, without microtranslating in the X-direction, istranslated back in the opposite Y-direction toward the upper edge 10′ ofthe sample 170. In particular, the sample 170 is accelerated in thenegative Y-direction under the control of the computer 100 along afourth beam path 720 to reach the predetermined sample translationvelocity Vpred prior to reaching the lower edge 10″ of the sample 170.Then, the sample 170 is continuously (i.e., without stopping) translatedin the negative Y-direction at the predetermined velocity Vpred so thatthe pulsed beamlets 164 continuously and sequentially irradiate thesample 170 along the entire length of a fifth beam path 725 (along thepath of the second beam path 705). When the pulsed beamlets 164 reachthe upper edge 10′ of the sample 170, the translation of the sample 170is slowed with respect to the pulsed beamlets 164 (in a sixth beam path730) until the beamlets 164 impinge on the first location 20. It shouldbe noted that after the pulsed beamlets 164 pass the upper edge 10′ ofthe sample 170, the entire portion of the sample 170 which wasirradiated along the second beam path 705 has undergone sequentialmelting and solidification. Accordingly, when this pass is completed,the surface of the sample 170 corresponding to the fifth beam path 725is partially melted and resolidified. In this manner, the resulting filmsurface may be further smoothed out. In addition, using this technique,the energy output of the pulsed laser beam 149 (and of the pulsedbeamlets 164) may be decreased to effectively smooth out the surface ofthe film. Similarly to the technique of FIG. 1b, a grainboundary-controlled polycrystalline silicon thin film area 540 forms inthe irradiated regions of the sample 170, a portion of which is shown inFIG. 5b. This grain boundary-controlled polycrystalline silicon thinfilm area 540 extends for the entire length of the second and fifthirradiated beam paths 705, 725. Again, it is not necessary to shut downthe pulsed laser beam 149 after the pulsed beamlets 164 have crossed thelower edge 10″ of the sample 170, and is no longer irradiates the sample170.

[0048] Thereafter, the sample 170 is microtranslated for a predetermineddistance (e.g., 3 micrometers) in the X-direction along a seventh beampath 735 until the pulse beamlets impinge on a third location 740, andis then again accelerated in the forward Y-direction (toward the loweredge 10″ of the sample 170) under the control of the computer 100 toreach the predetermined velocity Vpred with respect to the pulsedbeamlets 164 along an eighth beam path 745. The pulsed beamlets 164reach an upper edge 10′ of the sample 170 when the velocity oftranslation of the sample 170 with respect to the pulsed beamlets 164reach the predetermined velocity Vpred. Then, the sample 170 iscontinuously (i.e., without stopping) translated in the forwardY-direction at the predetermined velocity Vpred so that the pulsedbeamlets 164 continuously and sequentially irradiate the sample 170 foran entire length of a ninth beam path 750. When the pulsed beamlets 164reach the lower edge 10″ of the sample 170, the translation of thesample 170 is slowed with respect to the pulsed beamlets 164 (in a tenthbeam path 760) until the pulsed beamlet 164 impinge on a fourth location765. It should be noted that after the final pulsed laser beam 164 passthe lower edge 10″ of the sample 170, the entire portion of the sample170 which was irradiated along the ninth beam path 750 has undergonesequential full melting and resolidification.

[0049] Thereafter, without microtranslating, the direction of thetranslation of the sample 170 is again reversed (via beam paths 770,775, 780), and these paths of the sample 170 are again each continuouslyand sequentially irradiated by continuously translating the sample 170in the reverse Y-direction (which also extends along the ninth beam path750) at the predetermined velocity Vpred. Accordingly, when this pass iscompleted, the surface of the sample 170 corresponding to the beam path775 is partially melted and resolidified. The surface of these paths745-780 is smoothed out as a result of the forward and reverseY-direction translation and irradiation along the same beam path of thesample 170 (without microtranslation). The final product of suchprocedure is the creation of large-grained, grain boundary-controlledcrystalized structure along the entire column (e.g., dimensioned 2 cm by40 cm) of the sample 170, having a flat (or flatter) surface.

[0050] Then, the sample 170 is stepped to the next column (i.e., thesecond column 6) until the beamlets impinge on a fifth location 790 viaanother beam path 785, and the sample 170 is allowed to settle to dampout any vibrations of the sample 170 and stage 180 that may haveoccurred when the sample 170 was stepped where the pulsed beamlets 164impinge on the fifth location 790. The procedure is repeated for allcolumns of the sample 170, similarly to the procedure described aboveand illustrated in FIG. 1b.

[0051] Referring next to FIG. 8, the steps executed by computer 100 tocontrol the thin silicon film crystallization growth method implementedaccording of the procedure shown in FIG. 1b and/or FIG. 7 is describedbelow. For example, various electronics of the system shown in FIG. 1aare initialized in step 1000 by the computer 100 to initiate theprocess. A thin amorphous silicon film sample on a substrate 170 is thenloaded onto the sample translation stage 180 in step 1005. It should benoted that such loading may be either manual or robotically implementedunder the control of the computer 100. Next, the sample translationstage 180 is moved into an initial position in step 1015, which mayinclude an alignment with respect to reference features on the sample170. The various optical components of the system are adjusted andfocused in step 1020, if necessary. The laser is then stabilized in step1025 to a desired energy level and pulse repetition rate, as needed tofully melt the amorphous silicon sample over the cross-sectional area ofeach pulsed beamlet incident on the sample in accordance with theparticular processing to be carried out. If necessary, the attenuationof the pulsed beamlets 164 is finely adjusted in step 1030.

[0052] Next, the shutter can be opened (or the computer activates toturn on the pulsed laser beam 149) in step 1035 to irradiate the sample170 by the pulsed beamlets 164 and accordingly, to commence thecontinuous motion sequential lateral solidification method illustratedin FIGS. 1b and 7. The sample is translated in the Y-directioncontinuously while a first beam path of the sample (e.g., the samplealong the second beam path 30) is continuously and sequentiallyirradiated (step 1040). The sample 170 is translated in the Y-directioncontinuously at the predetermined velocity Vpred while a second beampath of the sample (e.g., the sample along the sixth beam path 55) issequentially and continuously irradiated (step 1045). With respect toFIG. 1b, this can be seen by the continuous translation of the sample170 along the second beam path 30 while the sample 170 is beingcontinuously and sequentially irradiated, then slowing down along thethird beam path 35, microtranslating the sample along the X-directionalong the fourth beam path 45, waiting for the sample 170 to settle,accelerating along the fifth beam path 50, and then continuouslytranslating the sample 170 along the sixth beam path 55 while the sample170 is being continuously and sequentially irradiated. In this manner,an entire column of the sample 170 is sequentially irradiated. If someportion of the current column of the sample 170 is not irradiated, thecomputer 100 controls the sample 170 to continuously translate at thepredetermined velocity Vpred in a particular direction so that anotherportion of the current column of the sample 170 which has not yet beenirradiated, is irradiated (step 1055).

[0053] Then, if the crystallization of an area of the sample 170 hasbeen completed, the sample is repositioned with respect to the pulsedbeamlets 164 in steps 1065, 1066 (i.e., moved to the next column orrow—the second column 6) and the crystallization process is repeated onthe new path. If no further paths have been designated forcrystallization, the laser is shut off in step 1070, the hardware isshut down in step 1075, and the process is completed in step 1080. Ofcourse, if processing of additional samples is desired or if the presentinvention is utilized for batch processing, steps 1005, 1010, and1035-1065 can be repeated on each sample. It is well understood by thosehaving ordinary skill in the art that the sample may also becontinuously translated in the X-direction, and microtranslated in theY-direction. Indeed, it is possible to continuously translate the sample170 in any direction so long as the travel paths of the pulsed beamlets164 are parallel, continuous and extend from one edge of the sample 170to another edge of the sample 170.

[0054] The foregoing merely illustrates the principles of the presentinvention. Various modifications and alterations to the describedembodiments will be apparent to those skilled in the art in view of theteachings herein. For example, the thin amorphous or polycrystallinesilicon film sample 170 may be replaced by a sample having pre-patternedislands of such silicon film. In addition, while the exemplaryembodiments above have been described for laser systems in which thelaser beams are fixed and preferably not scannable, it should berecognized that the method and system according to the present inventioncan utilize a pulsed laser beam which can be deflected at a constantspeed along a path of a fixed sample. It will thus be appreciated thatthose skilled in the art will be able to devise numerous systems andmethods which, although not explicitly shown or described herein, embodythe principles of the present invention, and are thus within the spiritand scope of the present invention.

What is claimed is:
 1. A method for processing a silicon thin filmsample to produce a crystalline silicon thin film, the film samplehaving a first edge and a second edge, the method comprising the stepsof: (a) controlling a laser beam generator to emit a laser beam; (b)masking portions of the laser beam to generate patterned beamlets, eachof the patterned beamlets impinging on the film sample and having anintensity which is sufficient to melt the film sample; (c) continuouslyscanning, at a first constant predetermined speed, the film sample sothat impingement of the patterned beamlets moves along a first path onthe film sample between the first edge and the second edge with thepatterned beamlets; and (d) continuously scanning, at a second constantpredetermined speed, the film sample so that impingement of thepatterned beamlets moves along a second path on the film sample betweenthe first edge and the second edge with the patterned beamlets.
 2. Themethod of claim 1 , wherein step (c) comprises: continuously translatingthe film sample so that the patterned beamlets sequentially irradiatefirst successive portions of the film sample along the first path,wherein the first portions are melted while being irradiated, andwherein step (d) comprises: continuously translating the film sample sothat the patterned beamlets sequentially irradiate second successiveportions of the film sample along the second path, wherein the secondportions are melted while being irradiated.
 3. The method of claim 2 ,wherein, after the film sample is translated along the first path toirradiate a next first successive portion of the film sample, thepreviously irradiated first portion is resolidified, and wherein, afterthe film sample is translated along the second path to irradiate a nextsecond successive portion of the film sample, the previously irradiatedsecond portion is resolidified.
 4. The method of claim 1 , wherein thefirst path is parallel to the second path, wherein, in step (c), thefilm sample is continuously scanned in a first direction, and wherein,in step (d), the film sample is continuously scanned in a seconddirection, the first direction being opposite to the second direction.5. The method of claim 1 , wherein the first edge is located on a sideof the film sample which is opposite from a side of the film samplewhere the second edge is located.
 6. The method of claim 2 , furthercomprising the steps of: (e) before step (d), positioning the filmsample so that the patterned beamlets impinge on at a first locationoutside of boundaries of the film sample with respect to the filmsample; and (f) after step (e) and before step (d), microtranslating thefilm sample so that impingement of the patterned beamlet moves from thefirst location to a second location, wherein step (d) is initiated whenthe patterned beamlets impinge on the second location.
 7. The method ofclaim 6 , further comprising the steps of: (g) after step (d),translating the film sample so that the patterned beamlets impinge on athird location which is outside the boundaries of the film sample; (h)after step (g), stepping the film sample so that impingement of thepatterned beamlets moves from the third location to a fourth location,the fourth location being outside of the boundaries of the film sample;and (i) after step (h), maintaining the film sample so that thepatterned beamlets impinge on the fourth location until any vibration ofthe film sample is damped out.
 8. The method of claim 7 , furthercomprising the step of: (j) after step (i), repeating steps (c) and (d)for respective third and fourth paths of the patterned beamlets on thefilm sample.
 9. The method of claim 2 , wherein, in step (c), the filmsample is continuously scanned in a first direction, and wherein, instep (d), the film sample is continuously scanned in a second direction,and further comprising the steps of: (k) after step (c), continuouslytranslating at the first constant predetermined speed the film sample sothat impingement of the patterned beamlets moves along the first path toreach a first location, wherein the patterned beamlets irradiate thefirst successive portions of the film sample, the film sample beingtranslated in a direction which is opposite to the first direction; (l)after step (k) and before step (d), microtranslating the film sample sothat impingement of the patterned beamlets moves from the first locationto a second location, the second location being outside of boundaries ofthe film sample; and (m) after steps (l) and (d), continuouslytranslating at the second constant predetermined speed the film sampleso that impingement of the patterned beamlets moves along the secondpath to reach the second location, wherein the patterned beamletsirradiate the second successive portions of the film sample, the filmsample being translated in a direction which is opposite to the seconddirection.
 10. The method of claim 9 , further comprising the steps of:(n) after step (m), stepping the film sample so that impingement of thepatterned beamlets moves from outside the boundaries of the film samplefrom the second location to a third location; and (o) maintaining thefilm sample so that the patterned beamlets impinge on the third locationuntil any vibration of the film sample is damped out.
 11. The method ofclaim 10 , further comprising the step of: (p) after step (p), repeatingsteps (c), (d), (k), (l) and (m) so that impingement of the patternedbeamlets moves along respective third and fourth paths on the filmsample.
 12. A system for processing a polycrystalline silicon thin filmsample into a crystalline thin film, the film sample having a first edgeand a second edge, the system comprising: a memory storing a computerprogram; and a processing arrangement executing the computer program toperform the following steps: (a) controlling a laser beam generator toemit a laser beam, (b) masking portions of the laser beam to generatepatterned beamlets, each of the patterned beamlets impinging on the filmsample having an intensity which is sufficient to melt the film sample,(c) continuously scanning, at a first constant predetermined speed, thefilm sample so that impingement of the patterned beamlets moves along afirst path on the film sample between the first edge and the second edgewith the patterned beamlets, and (d) continuously scanning, at a secondconstant predetermined speed, the film sample so that impingement of thepatterned beamlets moves along a second path on the film sample betweenthe first edge and the second edge with the patterned beamlets.
 13. Thesystem of claim 12 , wherein, during the execution of step (c), theprocessing arrangement continuously translates the film sample so thatimpingement of the patterned beamlets moves along the first path,wherein the patterned beamlets irradiate successive first portions ofthe film sample, the first portions being melted while being irradiated,and wherein, during the execution of step (d), the processingarrangement continuously translates the film sample so that impingementof the patterned beamlets moves along the second path, wherein thepatterned beamlets irradiate successive second portions of the filmsample, the second portions being melted while being irradiated.
 14. Thesystem of claim 13 , wherein, after the processing arrangement causesthe translation of the film sample so that the patterned beamletsirradiate a next first successive portion along the first path of thefilm sample, the previously irradiated first portion along the firstpath is resolidified, and wherein, after the processing arrangementcauses the translation of the film sample so that the patterned beamletsirradiate a next successive second portion along the second path of thefilm sample, the previously irradiated second portion along the secondpath is resolidified.
 15. The system of claim 12 , wherein the firstpath is parallel to the second path, wherein, while executing step (c),the processing arrangement causes the film sample to be continuouslyscanned in a first direction, and wherein, while executing step (d), theprocessing arrangement causes the film sample to be continuously scannedin a second direction, the first direction being opposite to the seconddirection.
 16. The system of claim 12 , wherein the first edge islocated on a side of the film sample which is opposite from a side ofthe film sample at which the second edge is located.
 17. The system ofclaim 13 , wherein the processing arrangement executes the followingadditional steps: (e) before step (d), positioning the film sample sothat the patterned beamlets impinge on a first location outside ofboundaries of the film sample with respect to the film sample, and (f)after step (e) and before step (d), microtranslating the film sample sothat impingement of the patterned beamlets moves from the first locationto a second location, and wherein the processing arrangement executesstep (d) with the patterned beamlets initially impinging on the secondlocation.
 18. The system of claim 17 , wherein the processingarrangement executes the following additional steps: (g) after step (d),translating the film sample so that impingement of the patternedbeamlets moves to a third location which is outside the boundaries ofthe film sample, (h) after step (g), stepping the film sample so thatimpingement of the patterned beamlets moves from the third location to afourth location, the fourth location being outside of the boundaries ofthe film sample, and (i) after step (h), maintaining the film sample sothat the patterned beamlets impinge on the fourth location until anyvibration of the film sample is damped out.
 19. The system of claim 18 ,wherein the processing arrangement executes the following additionalstep: (j) after step (i), repeating steps (c) and (d) for impingement ofthe patterned beamlets along respective third and fourth paths on thefilm sample.
 20. The system of claim 13 , wherein, while executing step(c), the processing arrangement continuously translates the film samplein a first direction, wherein, while executing step (d), the processingarrangement continuously translates the film sample in a seconddirection, and wherein the processing arrangement executes the followingadditional steps: (k) after step (c), continuously translating at thefirst constant predetermined speed the film sample so that impingementof the patterned beamlets moves along the first path to reach a firstlocation, wherein the patterned beamlets sequentially irradiate thefirst successive portions of the film sample, the film sample beingtranslated in a direction which is opposite to the first direction, (l)after step (k) and before step (d), microtranslating the film sample sothat impingement of the patterned beamlets moves from the first locationto a second location, the second location being provided outside ofboundaries of the film sample, and (m) after steps (l) and (d),continuously translating at the second constant predetermined speed thefilm sample so that impingement of the patterned beamlets moves alongthe second path to reach the second location so that the patternedbeamlets sequentially irradiate the second successive portions of thefilm sample, the film sample being translated in a direction which isopposite to the second direction.
 21. The system of claim 20 , whereinthe processing arrangement executes the following additional steps: (n)after step (m), stepping the film sample so that impingement of thepatterned beamlets moves from outside the boundaries of the film samplefrom the second location to a third location, and (o) maintaining thefilm sample so that the patterned beamlets impinge on the third locationuntil any vibrating of the film sample is damped out.
 22. The system ofclaim 21 , wherein the processing arrangement executes the followingadditional step: (p) after step (p), repeating steps (c), (d), (k), (l)and (m) for moving the impingement of the patterned beamlets alongrespective third and fourth paths on the film sample.